A structure such as a bridge is inspected.
A related technology is disclosed in Japanese Laid-open Patent Publication No. 2012-208043 or Non-Patent Document: Tsutomu Yoshioka, Masahiko Harada, Hiroki Yamaguchi, and Shin Itou, “A study on the vibration characteristics change of the steel truss bridge by the real damage of diagonal member,” Journal of Structural Engineering, (Japan), Japan Society of Civil Engineers, March 2008, VOL. 54A, pp. 199-208.